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Universal domain wall dynamics under electric field in Ta/CoFeB/MgO devices with perpendicular anisotropy

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      Abstract

      Electric field effects in ferromagnetic metal/dielectric structures provide a new route to control domain wall dynamics with low-power dissipation. However, electric field effects on domain wall velocities have only been observed so far in the creep regime where domain wall velocities are low due to strong interactions with pinning sites. Here we show gate voltage modulation of domain wall velocities ranging from the creep to the flow regime in Ta/Co 40Fe 40B 20/MgO/TiO 2 structures with perpendicular magnetic anisotropy. We demonstrate a universal description of the role of applied electric fields in the various pinning-dependent regimes by taking into account an effective magnetic field being linear with the electric field. In addition, the electric field effect is found to change sign in the Walker regime. Our results are consistent with voltage-induced modification of magnetic anisotropy. Our work opens new opportunities for the study and optimization of electric field effect at ferromagnetic metal/insulator interfaces.

      Abstract

      Domain walls in ferromagnetic–oxide structures can be moved using an electric field, which could be useful for low-power electronic devices. Here, the authors demonstrate the modulation of the velocity of these domain walls between a creep and a flow regime.

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      Most cited references 15

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      Magnetic domain-wall racetrack memory.

      Recent developments in the controlled movement of domain walls in magnetic nanowires by short pulses of spin-polarized current give promise of a nonvolatile memory device with the high performance and reliability of conventional solid-state memory but at the low cost of conventional magnetic disk drive storage. The racetrack memory described in this review comprises an array of magnetic nanowires arranged horizontally or vertically on a silicon chip. Individual spintronic reading and writing nanodevices are used to modify or read a train of approximately 10 to 100 domain walls, which store a series of data bits in each nanowire. This racetrack memory is an example of the move toward innately three-dimensional microelectronic devices.
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        A perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction.

        Magnetic tunnel junctions (MTJs) with ferromagnetic electrodes possessing a perpendicular magnetic easy axis are of great interest as they have a potential for realizing next-generation high-density non-volatile memory and logic chips with high thermal stability and low critical current for current-induced magnetization switching. To attain perpendicular anisotropy, a number of material systems have been explored as electrodes, which include rare-earth/transition-metal alloys, L1(0)-ordered (Co, Fe)-Pt alloys and Co/(Pd, Pt) multilayers. However, none of them so far satisfy high thermal stability at reduced dimension, low-current current-induced magnetization switching and high tunnel magnetoresistance ratio all at the same time. Here, we use interfacial perpendicular anisotropy between the ferromagnetic electrodes and the tunnel barrier of the MTJ by employing the material combination of CoFeB-MgO, a system widely adopted to produce a giant tunnel magnetoresistance ratio in MTJs with in-plane anisotropy. This approach requires no material other than those used in conventional in-plane-anisotropy MTJs. The perpendicular MTJs consisting of Ta/CoFeB/MgO/CoFeB/Ta show a high tunnel magnetoresistance ratio, over 120%, high thermal stability at dimension as low as 40 nm diameter and a low switching current of 49 microA.
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          Current-driven dynamics of chiral ferromagnetic domain walls

          In most ferromagnets the magnetization rotates from one domain to the next with no preferred handedness. However, broken inversion symmetry can lift the chiral degeneracy, leading to topologically-rich spin textures such as spin-spirals and skyrmions via the Dzyaloshinskii-Moriya interaction (DMI). Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy metal and an oxide, the DMI stabilizes chiral domain walls (DWs) whose spin texture enables extremely efficient current-driven motion. We show that spin torque from the spin Hall effect drives DWs in opposite directions in Pt/CoFe/MgO and Ta/CoFe/MgO, which can be explained only if the DWs assume a N\'eel configuration with left-handed chirality. We directly confirm the DW chirality and rigidity by examining current-driven DW dynamics with magnetic fields applied perpendicular and parallel to the spin spiral. This work resolves the origin of controversial experimental results and highlights a new path towards interfacial design of spintronic devices.
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            Author and article information

            Affiliations
            [1 ]Center for Nanoscience and Nanotechnology, Université Paris-Sud–CNRS, UMR 9001 , 91405 Orsay, France
            [2 ]Singulus Technologies AG , 63796 Kahl am Main, Germany
            [3 ]Center for Memory and Recording Research, University of California San Diego , La Jolla, California 92093, USA
            Author notes
            Journal
            Nat Commun
            Nat Commun
            Nature Communications
            Nature Publishing Group
            2041-1723
            16 November 2016
            2016
            : 7
            27848936
            5116098
            ncomms13532
            10.1038/ncomms13532
            Copyright © 2016, The Author(s)

            This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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